Land

"Landmass" redirects here. For the ambient album by Steve Roach, see Landmass (album).

This article may require copy editing for grammar, style, cohesion, tone, or spelling. You can assist by editing it.(February 2014)

Map showing Earth's land areas, in shades of green and yellow.

Land rising from the sea.

Land, sometimes referred to as dry land, is the solid surface of the Earth that is not permanently covered by water.[1] The vast majority of human activity occurs in land areas that support agriculture, habitat, and various natural resources.

Areas where land meets large bodies of water are called coastal zones. The division between land and water is a fundamental concept to humans, and can have strong cultural importance. The demarcation between land and water varies by local jurisdiction. A maritime boundary is one such political demarcation. A variety of natural boundaries exist to help define where water meets land. Solid rock landforms are easier to demarcate than marshy or swampy boundaries, where there is no clear point at which the land ends and a body of water has begun. Demarcation can further vary due to tides and weather.

The crust, which currently forms the Earth's land, was created when the molten outer layer of the planet Earth cooled to form a solid mass as the accumulated water vapor began to act in the atmosphere. Once land became capable of supporting life, biodiversity evolved over hundreds of million years, expanding continually except when punctuated by mass extinctions.[10]

The two models[11] that explain land mass propose either a steady growth to the present-day forms[12] or, more likely, a rapid growth[13] early in Earth history[14] followed by a long-term steady continental area.[15][16][17] Continents formed by plate tectonics, a process ultimately driven by the continuous loss of heat from the Earth's interior. On time scales lasting hundreds of millions of years, the supercontinents have formed and broken apart three times. Roughly 750 mya (million years ago), one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 mya, then finally Pangaea, which also broke apart 180 mya.[18]

"Land mass" refers to the total surfacearea of the land of a geographical region or country (which may include discontinuous pieces of land such as islands). It is written as two words to distinguish it from the usage "landmass" —the contiguous area of land surrounded by ocean.

The Earth's total land mass is 148,939,063.133 km2 (57,505,693.767 sq mi) which is about 29.2% of its total surface. Water covers approximately 70.8% of the Earth's surface, mostly in the form of oceans.

In early Egyptian[20] and Mesopotamian thought, the world was portrayed as a flat disk floating in the ocean. The Egyptian universe was pictured as a rectangular box with a north-south orientation and with a slightly concave surface, with Egypt in the center. A similar model is found in the Homeric account of the 8th century BC in which "Okeanos, the personified body of water surrounding the circular surface of the Earth, is the begetter of all life and possibly of all gods."[21] The biblical earth is a flat disc floating on water.[22]

The Pyramid Texts and Coffin Texts reveal that the ancient Egyptians believed Nun (the ocean) was a circular body surrounding nbwt (a term meaning "dry lands" or "islands"), and therefore believed in a similar Ancient Near Eastern circular Earth cosmography surrounded by water.[23][24][25]

The spherical form of the Earth was suggested by early Greek philosophers, a belief espoused by Pythagoras. Contrary to popular belief, most people in the Middle Ages did not believe the Earth was flat: this misconception is often called the "Myth of the Flat Earth". As evidenced by thinkers such as Thomas Aquinas, the European belief in a spherical Earth was widespread by this point in time.[26] Prior to circumnavigation of the planet and the introduction of space flight, belief in a spherical Earth was based on observations of the secondary effects of the Earth's shape and parallels drawn with the shape of other planets.[27]

Most planets known to humans are either gaseous Jovian planets or solid terrestrial planets. Terrestrial planets include Mercury, Venus, Earth, and Mars. These inner planets have a rocky surface with metal interiors.[28] The Jovian planets consist of Jupiter, Saturn, Uranus, and Neptune. While these planets are larger, their only land surface is a small rocky core surrounded by a large, thick atmosphere.[29] The gas giants, Jupiter and Saturn, are thought to have surface layers composed of liquid hydrogen rather than solid land; however, their planetary geology is not well understood. The possibility of Uranus and Neptune (the ice giants) possessing hot, highly compressed, supercritical water under their thick atmospheres has been hypothesised. While their composition is still not fully understood, a 2006 study by Wiktorowicz et al. ruled out the possibility of such a water "ocean" existing on Neptune,[30] though some studies have suggested that exotic oceans of liquid diamond are possible.[31] The entire surface of a rocky planet or moon is considered land, even with a lack of seas or oceans for contrast. Planetary bodies that have a thin atmosphere often have land that is marked by impact craters since atmospheric conditions would normally break-down incoming objects and erode rough impact sites. [32] Land on planetary bodies other than earth can also be bought and sold although ownership of extraterrestrial real estate is not recognized by any authority.[33]

The land of the Earth interacts with and influences climate heavily since the land surface heats up and cools down faster than air or water.[34]Latitude, elevation, topography, reflectivity, and land use all have varying impacts. The latitude of the land will influence how much solar radiation reaches the surface. High latitudes receive less solar radiation than low latitudes.[34] The height of the land is important in creating and transforming airflow and precipitation on Earth. Large landforms, such as mountain ranges, divert wind energy and make the air parcel less dense and able to hold less heat.[34] As air rises, this cooling effect causes condensation and precipitation. Reflectivity of the earth is called planetary albedo. The type of land cover that receives energy from the sun has an impact on the amount of energy that is reflected or transferred to Earth.[35]Vegetation has a relatively low albedo meaning that vegetated surfaces are good absorbers of the sun’s energy. Forests have an albedo of 10-15% while grasslands have an albedo of 15-20%. In comparison, sandy deserts have an albedo of 25-40%.[35] Land use by humans also plays a role in the regional and global climate. Densely populated cities are warmer and create urban heat islands that have effects on the precipitation, cloud cover, and temperature of the region.[34]

^The picture of the universe in Talmudic texts has the Earth in the center of creation with heaven as a hemisphere spread over it. Biblical writings, such as the Genesis creation story and the various Psalms that extol the firmament, the stars, the sun, and the earth, give similar explanations. The Hebrews saw the earth as an almost flat surface consisting of a solid and a liquid part and the sky as the realm of light in which heavenly bodies move. The earth rested on cornerstones and could not be moved except by Jehovah (as in an earthquake). According to the Hebrews, the sun and the moon were only a short distance from one another. "Cosmology." Encyclopedia Americana. Grolier Online, 2012. Author: Giorgio Abetti, Astrophysical Observatory of Arcetri-Firenze.

^The Earth is usually described as a disk encircled by water. Cosmological and metaphysical speculations were not to be cultivated in public nor were they to be committed to writing. Rather, they were considered to be "secrets of the Torah not to be passed on to all and sundry" (Ketubot 112a). While study of God's creation was not prohibited, speculations about "what is above, what is beneath, what is before, and what is after" (Mishnah Hagigah: 2) were restricted to the intellectual elite. (Topic Overview: Judaism, Encyclopedia of Science and Religion, Ed. J. Wentzel Vrede van Huyssteen. Vol. 2. New York: Macmillan Reference USA, 2003. p477-483. Hava Tirosh-Samuelson).

^Pyramid Texts, Utterance 366, 629a-629c: "Behold, thou art great and round like the Great Round; Behold, thou are bent around, and art round like the Circle which encircles the nbwt; Behold, thou art round and great like the Great Circle which sets."(Faulkner 1969, 120)